The present invention relates to a method for compressing data of two-value picture image, especially digital data of an original character pattern for a phototype setting by an electronic computer.
In a conventional method, a digital original character pattern for a phototype setting by an electronic computer is composed by a dot matrix having a high density since such a original character pattern is necessarily enlarged, differing from a character for a Chinese character word processor.
When the original character pattern expressed by a bit pattern of the dot matrix having the high density is processed as in the form of the bit pattern, a great number of bit numbers are required for storing one character. For example, a high density of 480.times.480=230400 bits is required to store one original character pattern for the phototype setting by the electronic computer.
As concerns the original character patterns for the phototype setting by the electronic computer, the style of type is important as well as the meaning as the normal characters, and various styles of type are required. Hence, the original character patterns are prepared as sets or fonts of styles of types such as the Ming type, the Gothic type, and so forth. Further, it is desired that the sets of styles of types of such original character patterns for the phototype setting by the electronic computer are filed so as to be always looked up.
However, as described above, when the bit pattern of one character is stored as the character data as it is, the very large memory capacity for filing the original character patterns is required. Accordingly, instead of storing the bit pattern as it is, the data for each character has been proposedly compressed by a zone compression technique for the picture electrical wireless transmission processing.
However, in a previously proposed run length system, only 20-30% amount of compression rate can be obtained. Meanwhile, in a vector system, several per cent of high compression can be obtained, but in a conventional compression processing the vector is obtained in the almost manually operation. Therefore, when the vector method is applied to the original character patterns for the phototype setting by the electronic computer, a lot of time and labor are necessary to perform the compression of the set of the original character patterns.
For example, in a conventional vector system, the character pattern is enlarged to a certain size so that the manual operation may be carried out, and points for producing the vectors by which the outline of the character pattern is approximated by straight lines, are plotted manually by using a digitizer.
In order to express the character pattern by the vectors, a lot of line segments are necessary, and particularly in case of the Ming-style type containing many curves, there are great many of the plotting points. Hence, in this case, a lot of time and labor are required, and further the great skill is necessary to plot such points.
Further, since this plotting operation is performed manually by the digitizer, in order to minimize the plotting errors, the character pattern for inputting, which is enlarged as far as possible, should be prepared. Further, the reforming operation of the finished character pattern is necessary at the end.